We want to exclude repair with tablet migrations to avoid races
between repair reads and writes with replica movement. Repair is not
prepared to handle topology transitions in the middle.
One reason why it's not safe is that repair may successfully write to
a leaving replica post streaming phase and consider all replicas to be
repaired, but in fact they are not, the new replica would not be
repaired.
Other kinds of races could result in repair failures. If repair writes
to a leaving replica which was already cleaned up, such writes will
fail, causing repair to fail.
Excluding works by keeping effective_replication_map_ptr in a version
which doesn't have table's tablets in transitions. That prevents later
transitions from starting because topology coordinator's barrier will
wait for that erm before moving to a stage later than
allow_write_both_read_old, so before any requets start using the new
topology. Also, if transitions are already running, repair waits for
them to finish.
Fixes#17658.
Fixes#18561.
98323be296